Replacement with position shift

Replacement of dilorine by alkyl groups with position shift... 

The spectra from strong oscillators have special features which are different from those from metallic and dielectric substrates. Different structures in tanf and A are observed on a metallic substrate, dependent on the thickness of the film (Fig. 4.65). For very thin films up to approximately 100 nm the Berreman effect is found near the position of n = k and n < 1 with a shift to higher wavenumbers in relation to the oscillator frequency. This effect decreases with increasing thickness (d > approx. 100 nm) and is replaced by excitation of a surface wave at the boundary of the dielectric film and metal. The oscillator frequency (TO mode) can now also be observed. On metallic substrates for thin films (d < approx. 2 pm) only the 2-component of the electric field is relevant. With thin films on a dielectric substrate the oscillator frequency and the Berreman effect are always observed simultaneously, because in these circumstances all three components of the electric field are possible (Fig. 4.66). 

If at least one of the aryl groups at 3 -position is replaced with an alkyl group, then the developed color is more reddish as a result of a hypso-chromic shift. Thus, 3 -diethylamino-6 -diphenylaminofluoran (35 R = C2H5)29 and 3 -diphenylamino-6 -(/V-ethyl-/i-toluidino)fluoran (35 R = 4-CH3C6H4)29 develop reddish violet and bluish violet colors, respectively. 

Typical pH-activity curves obtained with gram-positive /3-lactamases and benzylpenicillin show maxima in the range of pH 6.0-7.0 with a rather sharp decline in the alkaline range (2). Recent data on gramnegative /3-lactamases (25,31, 43, 44,59,65,90,94-96) show optimal values scattered over the range of pH 5.0-8.5. A shift in the pH-activity curve has been observed when benzylpenicillin was replaced with 6-APA (78,79) or methicillin (54) but not with cephalosporin C (31). 

Removal (formally) of the P-furan substituents has some effect on the spectral characteristics of the oxasapphyrins. In the case of the monoxasapphyrin 5.72, the position of the Soret band of the free-base appears relatively unchanged when compared to 5.21 or 5.74. However, protonation with HCl results in a slight red-shift of the Soret bands (to 445/453 nm), while protonation with HF results in a more pronounced Soret band splitting ( imax = 436 and 460 nm). ° If two of the pyrroles of pentaazasapphyrin are formally replaced with P-unsubstituted furans (e.g., 5.68), the Soret bands of both the free-base and protonated forms of the macrocycle shift to the blue by ca. 15 nm, relative to the P-substituted dioxa system 5.75. In this latter instance, however, the Soret band does not split upon protonation. 

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